Initiating a full discovery for a large topology can take a considerable amount of time, ranging from 1 hour to 2 or more hours, depending on the actual size of the topology. Keep this in mind when scheduling full discovery for the IP Manager.
Also, consider scheduling automatic full discovery during off hours (5:00 in the morning, for example). The VMware Smart Assurance IP Manager Deployment Guide recommends scheduling full discovery at least weekly and pending discovery at least daily. Typically, the duration of a pending discovery is much shorter than the duration of a full discovery.
Running the discovery more often will provide a more accurate network topology, but will also cost more in terms of network and system resources.